Diagnosis and Treatment of Chronic Ankle Instability

Ankle sprains involve up to 30% of all sport injuries. About 30% of patients may develop chronic ankle instability (CAI), which significantly limits their professional or recreational activities. The diagnosis of CAI relies on the understanding of anatomy and a thorough assessment of the patient. Imaging studies, including plain radiographs, sonography, MRI, and arthroscopic examinations, are beneficial in evaluating the extent and structures involved. Once conservative treatment has failed, surgery is indicated to restore ankle joint stability. Suture repair is sufficient, whether open or arthroscopically, if the remnant ligament quality is acceptable. Anatomical graft reconstruction is used for poor remnant quality or revision.


Introduction
Ankle sprains are among the most common of sports injuries, and lateral ankle sprains comprise more than 80% of these [1]. Even though most of them heal well with conservative treatment, a 56-74% recurrence rate has been reported [2]. Up to 30% of patients with lateral ankle sprains end up having chronic ankle instability (CAI) [3]. The predictors of patients with single or repeated ankle sprains who may develop CAI include a grade II-III sprain [4], postural instability [5], lower limb muscle weakness or imbalance [6], and decreased ankle dorsiflexion [7].

Pathophysiology
The pathophysiology of CAI includes anatomical and/or functional deficiencies. Anatomical factors consist of pathological laxity of ankle ligaments and problematic bony structures such as hindfoot varus [8,9]. Functional factors include neuromuscular and proprioception impairments [6,10].
The traditional spectrum of CAI is divided to mechanical instability, which means a structurally unstable ankle and functional instability, which means a perceptionally unstable ankle. Mechanical instability of the ankle can be demonstrated manually or subjectively. Functional instability is much more difficult to evaluate; a comprehensive questionnaire is usually needed for better communication and understanding [11].  [68]).
If the ATFL does not heal well after rupture, its laxity will result in excessive plantarflexion and supination of the ankle, which decreases the stability of the joint, increases the compensative burden of peroneal muscles, and increases the wearing of articular cartilage. Even after healing, some patients may still have lateral ankle pain and swelling despite their return of full pre-injury activity. The presence of local painful scarring, synovitis, post-traumatic weakness of peroneal muscles, and injury to the proprioception afferent fibers inside the ATFL may be the causative reasons of these residual symptoms.
The deltoid ligament is composed of a superficial layer and a deep layer. The superficial layer, which is positioned across the ankle and subtalar joint, consists of four components: the tibionavicular ligament, the tibiospring ligament, the tibiocalcaneal ligament, and the superficial posterior tibiotalar ligament [20]. The deep layer, which is thicker and positioned across the ankle joint only, consists of two components: the anterior tibiotalar ligament and the deep posterior tibiotalar ligament (Figure 2).
The deltoid ligament complex is composed of the deltoid ligament and the spring ligament (the calcaneonavicular ligament). The spring ligament helps not only to maintain the supination of midfoot but also to support the medial ankle structure through its connection with the deltoid ligament by the tibiospring ligament. A patient with MAI often presented with dysfunction of these two structures.

Neuromuscular structure
The peroneal musculature is the dynamic stabilizer of the lateral ankle joint. Lateral ankle sprains may cause injury to the ATFL as well as to the peroneal muscles. Not only can the muscular fibers be injured, the neuromuscular function can also be affected. It has been reported that the reaction time of the peroneal muscles may be delayed in patients with a history of repeated sprains, which may increase the risk of another lateral ankle sprain when the ankle lands in a supinated position [21]. This delay may be related to the deafferentation of receptors in the muscle tendon and ligaments around the ankle joint after a sprain injury [22].
Proprioception deficits are frequently encountered in patients with CAI. The dysfunction of proprioception will result in poor joint position sense, which means  (6) anterior colliculus, (7) posterior colliculus, (8) intercollicular groove, (9) sustentaculum tali, (10) medial talar process, (11) lateral talar process, (12)  in a patient with CAI that the actual ankle joint position may be much more inverted than perceived by the patient [23]. This error in joint position sense may increase the risk of lateral ankle sprains.

Diagnosis of chronic ankle instability
The diagnosis of CAI is mostly a clinically based diagnosis. There is no generally accepted standard of "how much laxity" is true unstable. The key idea is trying to determine whether the condition of instability could be the leading cause of the symptoms of the patient.

Presenting symptoms
The symptoms of CAI may be vague and nonspecific. Typical complaints are "insecurity" and "giving way" when running or walking on uneven ground. Patients may also complain of recurrent pain, swelling, and tenderness over medial or lateral ankle after prolonged standing or walking. Repeated ankle sprains are also a common complaint.
It should be noted that about 30% of the patients with CAI may be asymptomatic between sprains, which makes it an easily missed diagnosis [24]. Symptoms related to tendinitis, osteochondral lesion of talus, and even arthrosis of ankle joint may also be presented in patients with CAI.

Physical examinations
A comprehensive examination to check for tender points, alignment, stability, calf tension, muscle power and balance, and joint range of motion is essential for patients with potential CAI.

Tender points
A thorough palpation of the ankle/foot is essential in the initial evaluation of patients with CAI. An understanding of the surface anatomy is crucial for the assessment of the involved structures.
The presence of tenderness just anterior to the fibula tip indicates inflammation of the ATFL. Tenderness on the anterolateral ankle mortise that could be elicited by passive dorsiflexion of the ankle indicates possible anterolateral ankle impingement of the Bassett's ligament frequently seen in patients with CAI [25]. Bony spurs secondary to ankle arthrosis could also be a cause of anterior ankle impingement.
Tenderness on the anteromedial aspect of the ankle could indicate an osteochondral lesion of the talus or coexisting deltoid ligament injury. Tenderness on the posterolateral ankle may point to peroneal tendinitis, whereas medial foot tenderness along the posterior tibia tendon or the spring ligament is prevalent in patients with MAI.
A posteromedial ankle tenderness located anterior to the Achilles tendon indicates a possible posterior ankle impingement. A recent study showed that CAI may increase the likelihood for surgery in athletes with os trigonum syndrome [26].

Stress tests
Manual stress tests such as anterior drawer test and talar tilt can be positive in patients with ligament laxity, but the reliability of these tests is doubted [27].
Several modifications of the stress tests have been postulated such as the varus talar tilt test combined with an internal rotation pivot stress (VTTT with IR) and the anterior talar palpation (ATP) test [28,29]. The VTTT with IR adds an internal rotational stress on the hindfoot with varus stress, which may better detect the rotational instability in ATFL deficiency judging from its orientation [28]. The ATP test increases the sensitivity of traditional anterior drawer test by pressing the examiner's thumb on the anterolateral ridge of the talus to better detect the anterior talar translation during the anterior draw [29].
The superficial deltoid ligament can be evaluated using the external rotation test. With the sitting patient's leg relaxed and hanging free, the degree of ankle external rotation of both legs can be compared manually. The eversion stress test can be used to assess the deep deltoid ligament by similar manner [30].

Plain radiographs and dynamic radiographs
Plain weight-bearing radiographs of the ankle and foot are essential in the evaluation of patients with CAI to exclude any bony lesions and malalignment. Osseous fragments on the medial or lateral malleolar tip may indicate ligamentous or retinacular avulsion.
Dynamic radiographs can be performed manually, intraoperatively, or using a Telos stress device to demonstrate the anterior drawer test, the talar inversion, and the eversion test (Figure 3). For lateral ankle ligaments, a stress radiograph is considered positive when more than 5°difference compared with normal ankle or more than 10°absolute varus tilt is observed [31].
Dynamic radiographs are useful for determining the extent of instability objectively and for documentation purposes. The reported specificity of dynamic radiographs is high, but their sensitivity is low [32]. A recent study showed that preoperative stress radiographic findings do not affect the clinical outcomes of CAI after surgical treatment [33]. Therefore, the dynamic radiographs are better suited for follow-up than for diagnosis.

Musculoskeletal sonography
Musculoskeletal sonography allows real-time evaluation of the integrity and laxity of ligaments. It can also be used to check for tenosynovitis and periarticular synovitis of the ankle.
Evidence of an acute sprain is found when the compact fibrillar pattern of the ligament is disrupted by edema or adjacent hematoma [34]. The accuracy of sonography for an acute sprain of the ATFL and CFL is reported to be 95 and 90%, respectively [35]. Ultrasound is also highly accurate for the assessment of deltoid ligament injury after supination-external rotation fractures of the ankle [36].
In patients with CAI, the sonogram may show loss of compact fibrillar pattern and complete disorganization of the ligamentous tissue or even nonvisualization (Figure 4) [34]. It can be used to detect small avulsion fractures in the malleolus frequently seen in patient with CAI. Stress ultrasound, either done in real-time or in combination with the drawer test, has been proposed. One study compared the relative diagnostic values of the anterior drawer test, stress radiography, stress ultrasound, and magnetic resonance imaging (MRI) using arthroscopic finding as the reference standard. The results showed 78.6% sensitivity of the anterior drawer test, 86% of the stress radiographs, and 100% of both stress ultrasound and MRI [37]. In view of the clinical availability and cost, sonography may well be the imaging tool of choice for the diagnosis of CAI [38].
The major drawback of sonography is its operator dependency and its lack of standards in the communication with other health-care professionals.

MRI
MRI is useful for the evaluation of ligament integrity, thickness, and bony attachment. Normal ligaments appear as low-signal-intensity structures often surrounded by high-signal-intensity fatty tissue [39]. The ATFL is best seen in the axial plane, while the CFL and the deltoid are best seen in the coronal plane. Chronic ligament injury usually presents with morphological changes on MRI such as heterogeneous, intra-substance signals, wavy contour, thinning or elongation, and poor visualization or absence of ligament ( Figure 5). The surrounding fatty tissue may show fibrosis with medium-signal-intensity or may show a synovitis with a high-signal-intensity [40].
The diagnostic sensitivity of MRI without contrast for ATFL rupture is reported to be 100%, whereas the specificity is only 50% [41]. MRI in combination with arthrography may improve the accuracy for diagnosing ATFL rupture to 100% [42].
MRI can also show the presence of concomitant intra-and periarticular pathologies such as osteochondral lesions, articular degeneration, bone marrow edema, tendon injury or tenosynovitis, and ankle impingement syndrome. However, MRI cannot be used to evaluate the mechanical stability of the ankle.

Arthroscopic examination
In the United States, nearly one-half of the patients undergo arthroscopic evaluation before ligament reconstruction [43]. Ankle arthroscopy can be performed under regional anesthesia without traction in an outpatient setting. It can provide information on the integrity, thickness, attachment, and laxity of the ligaments around the ankle joint. It can also aid in the detection of intra-articular lesions such as injuries to the articular cartilage, bony or soft tissue impingement, and syndesmosis [16,[44][45][46][47]. In ATFL and deltoid ligament injuries, the most common site of avulsion is found at the proximal insertion at the anterior aspect of fibula. The examiner can often see a bare patch of the periosteum normally covered by ligament insertion on the medial or lateral malleolus. Many authors recommended a functional arthroscopic test, which includes axial traction to quantify the tibiotalar opening, anterior drawer test, and varus and valgus tilt test [48,49].
Using visual inspection and probe testing, injury to the ATFL can be classified in four grades (Figure 6) [50]: Grade 0, which represents a normal and continuous ligament with normal thickness and tautness Grade 1, a distended ligament with normal thickness but decreased tension by hook palpation Grade 2, a fibular or talar avulsion (with fibrous tissue) of the ATFL, normal thickness, but decreased tension by hook palpation Grade 3, a thin ATFL ligament with no mechanical resistance by hook palpation, with or without scar tissue Grade 4, which shows as scar tissue with no residual ligament and leaving a bald malleolus The author also postulated different surgical strategies according to different grading. Surgical repair and reconstruction techniques are still under debate as will be discussed later.

Conservative treatment
Conservative treatment is usually reserved for the correction of proprioception deficits, balance deficits, and any static disorders. A meta-analysis showed rehabilitation attempts, including balance training, manipulation, and muscle stretch/ training, which are beneficial by health-related quality of life standards in patients with CAI [51]. It has also been reported that patients with primarily functional instability are more likely to benefit from rehabilitation than patients with primarily mechanical instability [52].

Operative treatment
Operative treatment is indicated when conservative treatment failed to resolve the patients' symptoms. Patients with higher physical demands are less likely to become asymptomatic with conservative measures. Patients with mechanical instability, repeated ankle sprains, osseous fragments in the malleolar region, and limitations in on-demand activities may benefit most from operative treatment. It has been reported that patients who received surgical repair showed better muscle endurance and postural stability than patients who had conservative treatment [53].
The goals of surgery are to reestablish ankle joint stability with reduced risk of future sprains in the short term and of articular degeneration in the long term.
Several surgical techniques to reestablish ankle joint stability have been reported either by open or arthroscopic approach. These techniques can be roughly divided into two categories: suture repair and graft reconstruction.

Suture repair
The Broström procedure is the gold standard for patients with CAI and comes with several modifications [24]. After exposure of the remnant ligaments, the ligaments are either folded (if elongated) or reattached (if detached) back to the distal fibula using suture anchors or transosseous sutures [54]. If the quality of the remnant ligament is poor or the quality of the repaired structure is unsatisfactory, the repair can be reinforced using the nearby inferior extensor retinaculum [55]. A complication of using inferior extensor retinaculum as augmentation is that it may cause a decrease in ankle plantarflexion or pain on plantarflexion after the surgery.
Osseous fragments in the lateral malleolar region should be removed if they cause pain or are detached. However, if the fragment size is large, removal may cause a considerable soft tissue defect, which may complicate later repair [56]. Therefore, screw fixation should be considered in cases of large-sized osseous fragments.
In patients with MAI, similar procedures are used to expose, fold, and reattach the remnant ligament to the medial malleolus. If the remnant tissue quality is poor, a periosteal flap reflected from medial malleolus can be used as augmentation. The key to repair the deltoid ligament is, first, to tie the sutures with the ankle in plantigrade position and, second, to avoid sutures through the deep and superficial deltoid ligaments [27]. Sutures across both layers of deltoid ligament may cause a decrease in ankle plantarflexion or pain on plantarflexion after the surgery.
Techniques for arthroscopy-assisted or all-inside repair of both medial and lateral ankle ligaments have been proposed over many years (Figure 7) [57][58][59]. In a recent review, the postoperative functional scores, patient's satisfaction, and surgery-related complications of open and arthroscopic lateral ankle ligament repair have been compared. Excellent results were shown for both open and arthroscopic surgical procedures in the treatment of the chronic ankle instability. The higher complication rate of arthroscopic procedures relative to open ones represents a major issue; however, this does not seem to affect the patient's satisfaction [60].

Graft reconstruction
Using tendon grafts to reconstruct the medial or lateral ligaments is indicated when local tissue quality is poor or in case of revision surgery.
Numerous graft reconstruction techniques have been reported. They can be divided into roughly two types: anatomical and nonanatomical reconstruction.
Anatomical reconstruction is intended to reproduce the course of the ATFL and CFL as anatomically as possible. The nonanatomical reconstruction, also called peroneus tenodesis, leads to nonphysiological intra-articular pressure peaks, sacrifices a dynamic stabilizer, and causes movement restrictions. It should therefore only be used when all other treatment options have failed [61]. Recent metaanalysis concluded that nonanatomical reconstruction may abnormally increase the inversion stiffness at the subtalar level [62].
Numerous graft options have been reported including the plantaris longus tendon, hamstrings tendon, and bone-tendon-bone grafts [63][64][65][66]. These tendon grafts are fixed to the malleolus, talus, and calcaneus in various ways including the suture anchor, interference screw, and endo-button. The remnant ligaments are debrided or left in situ. There is still a lack of consensus as to which technique is biomechanically stronger or gives better functional results.

Postoperative treatment
Postoperative treatments of both suture repair and graft reconstruction are similar to that of acute ankle sprain. Recommendations according to the Cochrane review are listed in Table 1 [67].

Conclusions
Ankle sprains are involved in up to 30% of all sport injuries with 30% of patients likely to develop CAI. These traumas can limit their professional or recreational activities significantly. The diagnosis of CAI is mainly clinically based. Sonography is cost-effective and allows real-time assessment of ligament integrity and laxity. Arthroscopic examination has the highest accuracy rate and allows direct visualization of both ligaments and intra-articular lesions.
Once conservative treatment has failed, surgery is indicated to restore ankle joint stability. Suture repair is satisfactory, whether performed open or arthroscopically if the remnant ligament quality is acceptable. Anatomical graft reconstruction is used if remnant quality is poor or a revision is required.

Conflict of interest
The authors declare no conflict of interest.